Identification and Purification of Distinct Isomerase and Decarboxylase Enzymes Involved in the 4-Hydroxyphenylacetate Catabolic Pathway of Escherichia coli

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Abstract
The possible involvement of an isomerase in the E. coli 4-hydroxyphenylacetate meta-cleavage pathway was studied. 5-Carboxymethyl-2-hydroxymuconate undergoes both spontaneous and enzyme-catalyzed isomerization to give 5-carboxymethyl-2-oxo-hex-3-ene-1,6-dioate, a compound with an absorbance maximum at 246 nm. The latter compound rather than the former is the substrate for a decarboxylase that produces 2-hydroxyhepta-2,4-diene-1,7-dioate. The isomerase and decarboxylase enzymes were purified to over 90% homogeneity. Mg2+ is required for the decarboxylase reaction but not for the isomerase.

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